This invention relates to a feeding device for advancing ferromagnetic sheet metal strips cut by a first rotary knife shaft pair of a roller knife cutter from a metal sheet, to a second rotary knife shaft pair for transverse severance. The feeding device includes a mechanism for depositing the sheet metal strips and at least one circulating carrier member.
Roller knife cutters for longitudinal and transverse severance (also known as double or duplex slitters) have two knife shaft pairs provided with roller or cutter knives. The axes of one knife shaft pair are--as seen in plan view axes--arranged perpendicularly to the axes of the other knife shaft pair, as disclosed in European Patent Application, Publication No. 0 208 564 A1. With the first knife shaft pair metal sheets, particularly for use in packaging are cut into strips and are stacked--practically without spacing between one another--on a depositing and transporting table situated downstream of the first knife shaft pair as viewed in the feed direction. At that location the strips have to be separated and individually fed to the second knife shaft pair in a direction perpendicularly to the feeding direction of the first knife shaft pair. For separating the strips and feeding them to the second knife shaft pair essentially two solutions are known.
In one type of conventional feeding device the sheet metal strips cut by the first knife shaft pair are deposited in planes of different heights. The height of the different planes (or steps) decreases in a stepped or terrace-like manner towards the second knife shaft pair, wherein each sheet metal strip cut from one metal sheet or plate is associated with its own step. The circulating carrier device is generally formed of two chains whose carrier pawls, corresponding to the various depositing stages, are at different heights and are identical on the left and righthand side. Along the chains, the distance between the carrier pawls is greater than the step length or, as the case may be, the strip width so that the strips are consecutively advanced to the second knife shaft pair in a manner separated from one another.
It is a disadvantage of a feeding device of the above-outlined type that the carrier pawls on the chain and the step plates have to be reset or even replaced in case of changing the format (for example, for a different strip width or plate number); this results in undesired down periods for the roller knife cutter. Further, since the carrier pawls engage the stationary strips with a constant speed, risks are high that the trailing edge of the strips will be damaged as it collides with the carrier pawls. Also, the individual strips cut from the same sheet are exposed to various depositing conditions (various drop height and thus various duration of fall).
In another type of feeding device, rotary bars are positioned above the conveying plane for the second knife shaft pair. With each sheet metal strip a separate rotary bar is associated. The strips are pushed by the first knife shaft pair onto the bars and the bars are successively rotated so that the strips individually fall onto the transporting plane for the second knife shaft pair. Circulating chains with mechanical, form-locking carrier pawls push the thus-separated strips forward towards the second knife shaft pair.
In such a feeding device too, in case of a format change of the strips significant retooling is required. Further, the transporting plane to the second knife shaft pair is obstructed from above. This is inconvenient when standstill periods caused by unintentional occurrences are to be eliminated. For controlling the rotary bars a complex drive arrangement is required and risks are again high that the carrier pawls collide with the trailing edges of the sheet strips. In case of a format change of sheet strips significant labor input is necessary for readjustment.